Dense Compound Particles for Low-Porosity Sintering Feedstock
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Solution Overview
Problem
Existing methods for producing feedstock compound particles for additive manufacturing, such as spray drying and freeze drying, are energy-intensive, produce porous and brittle particles, and result in inhomogeneous distributions of sinterable material and binder, leading to poor flowability and porosity issues.
Innovation Solution
Compound particles comprising pulverulent non-organic particles in a temporary organic binder with specific density, shape, and distribution, achieved through a process that minimizes energy consumption and ensures homogeneous distribution and low porosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If spray drying or freeze drying processes are used to produce feedstock compound particles, then the particles can be formed with binder distribution, but the processes are energy-consuming and produce porous and brittle particles with inhomogeneous distribution
Solution Approach 1:
The patent changes the physical-chemical parameters of the binder system by using a thermoplastic binder that melts at a specific temperature range. By controlling the melting temperature and viscosity of the binder, the process achieves homogeneous particle formation without requiring the high energy input of spray drying or freeze drying. The binder melts and uniformly coats the sinterable particles during the granulation process, eliminating the need for energy-intensive drying steps while ensuring homogeneous distribution.
Solution Approach 2:
The invention utilizes the phase transition of the thermoplastic binder from solid to liquid state during heating. As the binder melts, it flows and uniformly distributes around the sinterable particles, creating homogeneous compound particles. This phase transition mechanism replaces the energy-intensive solvent evaporation in spray drying with a controlled melting process that occurs at lower temperatures and consumes less energy.
2Shape
If spray drying process is used, then particles can be formed, but shrinkage of the particle and migration of binder during drying leads to voids and shell-like structures
Solution Approach 1:
The patent modifies the processing parameters by eliminating the drying step entirely and instead using a melting approach. The thermoplastic binder is heated to its melting point, where it becomes fluid and uniformly distributes around the sinterable particles. This prevents the shrinkage and binder migration issues that occur during spray drying, as the binder is already in a mobile liquid state during particle formation rather than attempting to distribute during solvent evaporation.
Solution Approach 2:
The invention performs the binder distribution action preliminarily during the granulation process itself, before any potential shrinkage or structural changes can occur. The thermoplastic binder is melted and distributed uniformly around the sinterable particles during particle formation, ensuring homogeneous composition is established early in the process. This preliminary uniform distribution prevents subsequent void formation or shell-like structures that would result from later shrinkage or binder migration.
3Ease of operation
If feedstock compound particles are produced with rounded shape for better flowability, then distribution efficiency improves, but particles having rounded shape may not be obtained by comminution of pre-formed bulk material
Solution Approach 1:
The patent segments the particle formation process into discrete steps: first forming the compound particles with the thermoplastic binder coating the sinterable particles, then allowing these segmented particles to flow and pack efficiently. The segmentation of the binder and sinterable material into distinct phases (liquid binder coating solid particles) naturally produces rounded, flowable particles without requiring complex comminution or shaping operations on pre-formed bulk material.
Solution Approach 2:
The invention utilizes fluid dynamics principles by employing a fluidized bed or similar pneumatic system during the granulation process. The upward airflow fluidizes the particle mixture, allowing the molten thermoplastic binder to uniformly coat the sinterable particles and facilitating the formation of rounded, flowable compound particles. This pneumatic assistance simplifies the manufacturing process compared to mechanical comminution while achieving the desired particle morphology for optimal flowability.
4Manufacturing precision
If compound particles are produced with low porosity for dense green parts, then building up dense parts improves, but particles having low porosity may not be obtained by spray-drying or spray-freezing
Solution Approach 1:
The patent changes the fundamental processing parameter from solvent-based drying to melt-based granulation. By using a thermoplastic binder with a controlled melting temperature and appropriate viscosity, the process forms dense compound particles directly during granulation without creating the porous structures typical of spray-dried particles. The molten binder flows into and fills the interstices between sinterable particles, eliminating voids and producing dense, low-porosity compound particles that sinter into dense green parts without requiring additional densification steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides feedstock compound particles with high apparent density, smooth surfaces, and uniform distribution, resulting in improved flowability and reduced porosity, enhancing the quality of green and sintered parts.
Implementation Method 1
compound particles comprising pulverulent non-organic particles in a temporary organic binder
Implementation Method 2
atomizing the liquefied dispersion to obtain atomized droplets
Implementation Method 3
the compound particles are sintered to form a green part
Data Source
AI summary
A plurality of compound particles for use in a shaping and sintering process, comprising pulverulent non-organic particles in a temporary organic binder, is characterized in that: (i) at least 80% of the pulverulent non-organic particles have a maximum dimension Amax in the range of from 10 nm to 500 μm, (ii) the amount of the temporary organic binder ranges from about 1 to 99 vol.-%, based on the total volume of the compound particles, (iii) at least 80% of the compound particles have a maximum dimension Bmax in the range of from 10 μm to 1000 μm, (iv) the compound particles have an apparent density of at least 70% of the true density, and (v) the compound particles have continuous external surfaces formed from pulverulent non-organic particles exposed at the external surfaces and temporary organic binder in the interstices between the pulverulent non-organic particles, the temporary organic binder presenting non-fractured surfaces. A process for preparing compound particles for use in a shaping and sintering process, comprises 1) providing a liquefied dispersion of pulverulent non-organic particles dispersed in a liquefied temporary organic binder, wherein at least 80% of the pulverulent non-organic particles have a maximum dimension Amax in the range of from 10 nm to 500 μm, 2) atomizing the liquefied dispersion to obtain atomized droplets, at least 80% of the atomized droplets having a maximum dimension B′max in the range of from 10 μm to 1000 μm, and 3) allowing the atomized droplets to solidify to obtain the compound particles.